1. Field
The present invention relates to an image display apparatus for carrying out zoom processing over an image to be displayed on a display unit, a method of controlling the image display apparatus, an image display program, and a computer readable recording medium recording the same.
2. Related Art
Conventionally, there is known a digital image processing apparatus such as an image photographing apparatus configured to photograph a subject by an imaging device, thereby generating a digital image (for example, a digital still camera) or an image display apparatus configured to display a digital image on a display unit (for example, an image viewer).
Moreover, some digital image processing apparatuses have a zoom function for increasing or reducing a subject contained in a digital image into an optional size. For example, the image photographing apparatus can photograph a subject in a desirable size by carrying out a zoom-in operation or a zoom-out operation. For instance, furthermore, the image display apparatus can increase or reduce, into a desirable size, a predetermined range of a digital image to be displayed (for example, a range including a subject).
Referring to the zoom function, conventionally, the following proposal is made, for example. In Japanese Unexamined Patent Publication No. 2011-166306 (published on Aug. 25, 2011), it is proposed to stepwise decrease a zoom speed toward a zooming target position based on a variation in a zoom position from a zooming initial position to the zooming target position.
In Japanese Unexamined Patent Publication No. 10-23313 (published on Jan. 23, 1998), moreover, it is proposed to change a view angle at a variable zoom speed depending on a variation in a size of a subject in automatic view angle control.
In Japanese Unexamined Patent Publication No. 2005-308836 (published on Nov. 4, 2005), furthermore, it is proposed to store a focal length (a zooming position) in last photographing and to decrease a speed for changing the focal length when a current focal length approximates to the stored focal length.
In the prior art described above, however, in some cases in which a user performs an operation for quickly setting image zooming to have a proper value, composition cannot be adjusted sufficiently properly, for example, a part of a subject unintentionally protrudes out of an area due to an excessive enlarging operation. For example, the techniques disclosed in the Japanese Unexamined Patent Publications Nos. 2011-166306, 10-23313 and 2005-308836 serve to carry out view angle control based on a variation in a size of a subject, a variation in a zooming position or a stored focal length and do not take a position of the subject into consideration.